Presently, there are over a thousand known lettuce varieties within the following groups: batavia lettuce, butterhead or head lettuce, iceberg lettuce, lollo lettuce, oakleaf lettuce, and romaine or cos lettuce. These lettuce varieties can be sub-divided into two different groups depending on heading characteristic, i.e. tight heading vs. non-heading. The drawback with most presently available lettuce varieties is the tight heading characteristic which prevents the removal of individual leaves, making these varieties unsuitable for the emerging whole leaf lettuce market. Further, the whole leaf lettuce market has been limited to the use of loose leaf and romaine lettuce types, and was not economically feasible for iceberg or other heading lettuces, as the tight heading characteristics of these lettuce types prevent the removal of individual leaves. As a result, there is an ongoing need and demand for improved lettuce varieties which are specifically designed to suit the needs and specifications of the whole leaf lettuce market.
Among the basic traits a lettuce variety needs to possess to be considered in the whole leaf lettuce market is a non-heading characteristic and an open growth habit, so that the leaves can be easily removed from the core or stem. The variety also must have a durable thick leaf texture and reduced or absent mid-rib, as the leaves must undergo one of many mechanical processes of being removed, washed, and dried without cracking or breaking. Through these processes, leaves with thin texture become wilted and easily damaged, and leaves with a large mid-rib are prone to breaking and splitting, shortening their shelf life or rendering them completely unusable. Typically, decay of the lettuce product starts on the thin areas of the leaf margins and in the mid-rib. This aging is noted by browning of the leaf margin, as well as pinking, and browning of the leaf mid-rib. By eliminating the mid-rib, and producing a thicker leaf structure, a product is produced that has a longer shelf life. Lastly, the whole leaf lettuce market specifies strict leaf sizes and quality standards, as the individual leaves are stacked and packaged under strict market specifications.